Tia,
Having fostered wild ducks before, and now raising my own domestic ducks (runners by the way!) I would suggest you give some thought now to what you are going to do with this little fellow in the long run, as that will influence how he grows up.
If you plan on returning him to the wild when he is grown (or just letting him fly off when he is ready), then you should keep human contact to a minimum and preserve his natural wariness of you (no cuddles, no hand feeding, etc
) He is already imprinted on a duck, so there is a good chance that he can be assimilated back to the wild in a few months. You should also check the local laws with regard to releasing wildfowl.
If you plan on keeping him, then of course do all the things you would with your own ducks, ensure lots of human contact, etc (cuddles
) but again, check with your local wildlife rescue what the law is on keeping wildfowl. I imagine it would be heartbreaking to fall in love with this little one, and then have to give him up to the authorities when he will be essentially domesticated.
Brilliant job you are doing there, he really is a lucky little guy!